1. Field of the Invention
The present invention relates to a method of manufacturing highly dense multi-layer printed wiring board by using the laser drilling.
2. Description of the Related Art
FIG. 2 shows a method of manufacturing a printed wiring board by using conventional laser drilling disclosed in Japanese Laid-Open Patent Publication Hei. 6-21619. According to the conventional method of manufacturing printed wiring board, perdetermined holes are drilled in a laminated base member 12 (hereinafter also referred to as prepreg) having a cover film 1 using a laser beam to form through holes 13. Next, a copper foil 8 is provisionally laminated on the laminated base member 12 by hot pressing, and the through holes 13 are filled with conductive paste 6 using a squeegee 14. The cover film 1 is then peeled off, and another copper foil 8xe2x80x2 is provisionally laminated thereon by hot pressing. Finally, the copper foils 8 and 8xe2x80x2 are patterned by etching to form circuit conductors 15 and 15xe2x80x2.
In the conventional method of manufacturing the printed wiring board, the circuit conductor is formed without curing the conductive paste provided for interlayer connection. Therefore, the resin contained in the prepreg flows through the step of heating, or is cured and contracts when it is cooled. Therefore, the wiring layer is distorted causing a deviation in position of the terminal region (hereinafter also referred to as a land) of the circuit conductor and dexlines in the reliability of conduction. Therefore, the wiring pattern is not finely formed, and accuracy of laser drilling is not utilized enough, imposing a limitation on the density of the printed wiring board.
This invention was accomplished in order to solve the above problem, and provides a method of manufacturing multi-layer printed wiring board, which suppresses deviation in position caused by compression and heating in the step of laminating interlayer insulating layers of the multi-layer printed wiring board, accomplishing a high precision in the laser drilling, and accomplishing the wiring of a higher density.
The method of producing multi-layer printed wiring board of this invention comprises the steps of:
(a) stacking to adhere an adhesive uncured resin sheet on at least one surface of an inner base plate having wiring layers on both surfaces thereof;
(b) irradiating a predetermined portion of said uncured resin sheet with a laser beam to form, in said uncured resin sheet, a through hole which is tapered in cross section to expose a connection portion of said wiring layer of said inner base plate;
(c) filling said through hole with a conductive material to form an interlayer conductor to render the front surface and the back surface of said uncured resin sheet conductive to each other;
(d) stacking to adhere a conductive film on the front surface of said uncured resin sheet containing the portion of forming said interlayer conductor;
(e) curing said uncured resin sheet; and
(f) patterning said conductive film into a predetermined wiring shape.
The method of producing multi-layer printed wiring board of this invention may further include the steps of stacking a non-adhesive resin sheet on the uncured resin sheet prior to irradiating the uncured resin sheet with the laser beam, and peeling off the non-adhesive resin sheet after the interlayer conductor has been formed.